Synthesis and thermal stability of benzoxazine nitroxides
Paola Astolfi1, Pierluigi Stipa
1S.I.M.A.U. Department-Chemistry Division, Università Politecnica delle Marche, I-60131 Ancona, Italy.
Abstract:
A new class of stable nitroxides (aminoxyls) having a 1,4-benzoxazine structure were synthesized and the corresponding thermal stability tested. All derivatives were stable in the entire range of temperatures employed, except those having a benzyl or a tert-butyl group at the β-position with respect to the aminoxyl function, which underwent radical fragmentation. Such a behavior allowed a kinetic study, carried out by means of EPR spectroscopy, to determine the corresponding rate constants and activation parameters (E(a)). Appropriate DFT calculations were performed for all nitroxides including also the thermally stable ones, in order to study the geometries of the fragmentation transition States as well as to compute the corresponding bond dissociation enthalpies (BDH), useful for further modeling purposes. The data obtained were interpreted on the basis of the relative stability of the leaving radical, according to the corresponding E(a) and BDH, whereas in the case of tert-butyl derivatives steric hindrance should play a determinant role, as evidenced by a comparison of the geometric, kinetic, and thermodynamic parameters upon the whole series.
More Related Videos
06:18Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate
Published on: April 24, 2018
10:42Preparation of N-(2-alkoxyvinyl)sulfonamides from N-tosyl-1,2,3-triazoles and Subsequent Conversion to Substituted Phthalans and Phenethylamines
Published on: January 3, 2018
Related Concept Videos
Electrophilic Aromatic Substitution: Nitration of Benzene
Reactions at the Benzylic Position: Oxidation and Reduction
meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H
Preparation of Amines: Reduction of Oximes and Nitro Compounds
Though catalytic hydrogenation can reduce nitrobenzenes, the reduction is nonselective in the presence of other functional groups. For instance, if nitrobenzene contains an aldehyde group,...
Nitrosation of Enols
Directing and Steric Effects in Disubstituted Benzene Derivatives
